Toll line remote group busy signaling



July'l9, 1949. G. w. MITCHELL TOLL LINE REMOTE GROUP BUSY SIGNALINGFiled Feb. l19, 1948 v:2 sheetssheet 1 INVENTOR.

GEORGE Vl MITCHELL Zziga ATTORN E Y July 19, 1949. G. w. MITCHELL. I I2,476,888

TOLL LINE REMOTE GROUP Busy SIGNALING Filed Feb. 19, 1948 2 sheets-sheet2 I I EXCHANGE A ExcHANGEB A. C. SOURCE EouI SIG' ExcILc LINE EouIR 5.

` LINES To sos. CHAIN I INE ExcILB- '21000 RLY. EQUIP. 64 TER I I 15 'r64 49 L 47 EXCHANGE c EP l 82 ausv sla a cHAIN m SERIES THRU CHAIN RLXSOFOTHER LINE EQUIP EicHANeE o INE EouII. NAIN RLY SCEG- sERIEs Trnu cHAINLEsIboF OTHER LINE 91 LINE EOUI 1N V EN TOR. GEORGE W. MITCI-ELL FIG.2 I

ATTORNEY EQ UIP.

N RLY ExcH. u l

BUSY SIG.

Patented July 19, 1949 TOLL LINE REMOTE GROUP BUSY SIGNALING George W.Mitchell, Ann Arbor, Mich., assigner to Automatic Electric Laboratories,Inc.,v Chlcago, Ill., a corporation of Delaware Application February 19,1948, Serial No. 9,413

Claims. 1

The present invention relates in general to supervisory circuitarrangements whereby group busy indication is given at distant exchangeswhenever a group of line (toll) circuits outgoing from a center, ortandem, exchange to another distant exchange become busy.

In a network of exchanges including a number of terminating exchangesand a tandem exchange common to the terminating exchanges, an operatorin a terminating exchange having need for a line circuit from the tandemexchange to another terminating exchange ordinarily must make an attemptto gain access to such a line circuit regardlessly of whether all of theline circuits to the other terminating exchange are in use. In theinstances where the operator receives busy indication when attempting toappropriate a line circuit of a group, she must make one or more'furtherattempts until a free line circuit is obtained.

Such repeated unsuccessful attempts result in loss of operator time andthe useless occupying of inter-exchange circuit facilities.

It is an object of the invention to overcome the above describeddeficiency in inter-exchange line circuit operation by providing a newand novel line circuit group busying arrangement wherein a group busysignal, related to a group of line circuits from a tandem exchange to aterminating exchange, is located in each other terminating exchangehaving access to said related line circuit group, and this group busysignal is operated Whenever all the line circuits of said group of linecircuits are simultaneously occupied.

A feature of the invention resides in the novel manner in which a linecircuit group busy signal in a terminating exchange is operated from thetandem exchange over one of the regular line circuits from the tandemexchange to the terminating exchange.

Another feature of the invention relates to the provision of more thanone line circuit group busy signal in a terminating exchange for givinggroup busy supervision of more than one line circuit group from thetandem exchange to more than one other terminating exchange, over a linecircuit, or circuits, of the group from the tandem exchange to the firstmentioned terminating exchange in a new and novel manner.

A further feature of the invention concerns a novel circuit arrangementwherein the superimposition of an alternating current of a nonvoicefrequency on a line circuit from the tanthe operation of a busy signalin the terminating exchange.

There are other objects and features of the invention'having to do forthe most part with the circuit details necessary to carry out theforegoing.

The various objects and features of the invention will be understoodbest from a perusal of the following description of the drawingscomprising Figs. 1 and 2, which show by means of the usual circuitdiagrams a suicient amount of apparatus to enable the invention to bedescribedA and understood. Y

Referring now to the drawings- Fig.v l is a single-line circuit diagramshowing a tandem exchange A having line circuits extending to threeterminating exchanges B, C and D, and also means for enabling callsinitiated in the tandem exchange and in any of the termi-A natingexchanges to seize a line circuit to one of the terminating exchanges.

Fig. 2 shows the tandem exchange, the three terminating exchanges, andthe line circuits of Fig. 1 and, in addition, means for applying analternating current, or currents, to certain of the line circuits forcausing the operation of related busy signals in the terminatingoflices.

Two'line circuits are shown in Figs. l and 2 from the tandem exchangeAto each of theY terminating'exchanges, line circuits for terminatingexchange B being designated by the reference characters I0 and I5, forterminating exchange C by the characters 20 and 25, and for terminatingexchange D by the characters 30 and 35. It should be understood,however, that any required number of line circuits may be providedbetween the tandem exchange and each terminating exchange.

Line circuit I0 terminates at the tandem exchange A in a line equipmentI2 and at terminating exchange Bin a line equipment I I. Similarly, linecircuit I5 terminates in line equipments I4 and I3 respectively at thetandem exchange and terminating exchange B: line circuits 20 and 25terminate respectively in line equipments 22 and 24 at the tandemexchange and in line equipments 2| and 23 at terminating exchange C; andline circuits 30 and 35 termi-- nate respectively in line equipments 32and 34 at the tandem exchange and in line equipments 3I and 33 atterminating exchange D. These line equipments may be of any well-knowntype and circuit arrangement, according to preference or requirementand, therefore, it is condeni exchange to a terminating exchange causes,Il sidered unnecessary todetail any particular arrangement in thisdisclosure. In Fig. 2 for the tandem exchange end, enough of a chaincircuit arrangement is shown associated with the line equipments yoftheline circuits for each terminat-k ing exchange to properly Ydemonstratethe functioning of the line circuit group busy supervision.

. The line the tandem exchange A (Fig. 1) may be of any conventionaltype of selector switch, but as deand automatic rotary movement. Theseline circuit selectorsl have one level of bank contacts multipliedtogether for each terminating exchange, and contacts in each bank level'are con,- nected to the line circuits from thetandem exV changeto therelated terminating exchange. It should be understood at this time thatWhile only one line-circuit selector is shown in Fig. 1 for each ofthefour exchanges, line circuit selectors are provided for each exchangeaccording to traine requirements. v c J v Y The Yselection units .1, I1,21 and .31 eachree spectively represent any desired` train ofconventional switches required in the related eX- circuit selectors s,is, 2s and se 5in AY pictedcomprise the Well-known Strower Selettorswitch having controlled vertical movement f .4rv Y Y B wishes to extenda connection to exchange C, then by means of thepositional equipment(not shown) of Yoperator unit I8 (Fig. 1) the operator controls theswitchtrain represented by selection unit I1 to select a free outgoingline selector in the tandem exchange A, which Vfree selector is nowassumed to be selector I-9 reached `over line circuit I5. Next,` theoperator controls selectorV I9 (by dialing the digit 2.). toV raise theassociated shaft and wipers of selector' I-B' to then second levelwhereupon selector I9 then automatically rotates of the selector, bank,

its, wipers into the second level ofthe `bank in VAa 'well-known manner.I'f line Ycircuit 20 out-r going vfrom tandemfexchange A to terminatingexchange C lis notin use at this time, then the j Wipers .of selector I9willstop on the first conchanges for selecting' a free linecircuitselector in the tandem exchange as represented by the referencevcharactersV 9,' I9,V 29 or 39. Since the present inventionis'notconcerned with the deV tails of such selection units or trains, itis considered unnecessary to include furtherl details of Y In theinstance of these operator units also, thepresent invention is notconcerned withthe exact details o f the operator positions and relatedpositional control equipment arrangements,"it`

being understood that .any well-known or conventional arrangement may beutilized. The alternating current source 51 (Fig. 2) may be of anyVwell-known type of generating equipment'capable of producing currents ofat least two, frequencies. It should be understood, how'- ever, that thetwo frequencies indicatedv for the generating equipment in Fig. 2 arefor explanatory purposes only and do' not impose any par-'- ticularlimitations or restrictions. n

The filters indicated by the reference characters 6I, 62, 63, (i4,` 65,66, 10,'15, 80, `85, 90 and 95 in Fig. 2 may be of any well-known typeof lter tuned Yto pass alternating current of a particular frequency.AsA in the ease of the alternating current generating equipment, thefrequencies indicated for the variousr filters are for explanatorypurposes only and 'correspondingly do-not impose any particularlimitationsv or restrictions. The busy signal equipments 1I, 16,8|,186,'9I and 96 in Fig. 2 each comprise any suitable'arrangement ofequipment and circuit arrangement capable of responding to an input ofalternating Y current (supplied bythe related filter* 10, 15, 80;

85, 90 or 95) and as a'result of'such response then causing theoperation oflthe related busy signal 12,1182, 81,92 and 91. Y

Having described the equipment and appara--v tus, a detailed descriptionof the operation will nowbe given. 'i i y'Assuming iirst` thatenoperator in exchange tacts ofthe second level of the bank, and theoperator equipment represented by unit VI8 is automatically connected toline circuit'20, 'also in a V"well-known manner. If, however, linecircuit-201s inv prior vuse. at Vthe time selector V |19 tests'fth'efirst contacts of the second level of thef'bank, theny the Wipers ofVselectorV L8 are automatically Arotated tothe second contact ofexchange-Chanalternatively control selector 29.A

to select either `line circuit 30 or 35-outgoing from 'tandemfvexchangefA to terminating exchangelD by dialing the digit 1 selector 29to raise' its wipers to the firstV level ofthe switch bank.' VIt' willalso be apparent that 'an'operator in exchange C can controlselector 29in tandem exchange A (over line'ci'rcuit'ZIi)V to select either linecircuits I0 or I5 to terminating exchange B','or to select either linecircuits 30v or 35 to terminating exchange D: that an operator inYexchange D canf control selector 39 in tandem exchange VA(over linecircuitr36) to Select either lineV circuits I0 orvI5'to terminatingexchange B, or toselect either line circuits '20 Gr.25 to terminatingYexchangel C; and that an y operator in tandem exchange A Vcan Y controloutgoing 4from"tandern'exchange A to terminating;

Selector. y9 (over line circuit l)Y to select eitherV line circuits IIIor I5 to,Y terminating exchange connect with line circuit `ISjthenrthechain re- V layer.; and 45 in line equipmentslz and I4 (Fig. 2)"arevoperated ina well-known manner to com-'- plete an obvious circuit torelay 40, causing relayl el)V to operate. Int armatures 4I and142,'relay lilY extendstheA alternating current Supplyfromgenthese'ffilters are tunedto pass alternating current of 11 0,000''cycle frequency; filter 63,'there,fore, causing the alternatingcurrentroflooo Ycycle Y frequency to fbesuperimposed on linecircuit 25exchange' C, and lter N causing the alternating and thereby cause' 1current of 10,000 cycle frequency to be superimposed on line circuit 30outgoing from tandem exchange A to terminating exchange D.

Filter 80 in bridge of line circuit 25 at exchange C is tuned to passalternating current of 10,000 cycle frequency and, therefore, causes thealternating current superimposed on line circuit 25 by means of filter63 to be extended to busy signal equipment 48|. Means (not shown)associated with busy signal equipmenty 8| responds to the impressedalternating current in a well-known manner, and other means (not shown)also associated with busy signal equipment 8| responsive to the actionof said first means of busy signal equipment 8| causes ground potentialto be extended to busy signal 82 thereby to complete the' circuit ofbusy signal B2. The glowing of busy signal 82 indicates to the operator,or operators, at exchange C that al1 of the line circuits (l0 and l5)outgoing from the tandem exchange to terminating exchange B are in use.Now should a demand for a connection from exchange C to exchange B beinitiated while line circuits l and I are in prior use, it will beunnecessary for an operator at exchange C to attempt to select a linecircuit from tandem exchange A to exchange B until busy signal 82 ceasesto glow. Operator time which would otherwise be expended in repeatedtesting is conserved, and useless occupations of line ycircuits fromexchange C to tandem exchange A are avoided.

Filter S0 in bridge of line circuit 30 at exchange D is also tuned topass alternating current of 10,000 cycle frequency, and therefore,causes the alternating current superimposed on line circuit 30 by meansof lter 64 to be extended to busy signal equipment 9|. As a result ofthe passing of 10,000 cycle alternating current to busy signal equipment9|, busy signal 92 is caused to glow in a manner similar to thatdescribed in the preceding paragraph for the glowing of busy signal 82at exchange C. The glowing of busy signal 92 indicates to the operator,or operators, at exchange D that all of the line circuits (I0 and I5)outgoing from tandem exchange A to terminating exchange B are in use. Asa consequence of this group busy supervision at exchange D, theconservation of operator time and the eicient occupation of the linecircuits from exchange D to tandem exchange A become realities.

Assuming now that line circuits and 25 outgoing from tandem exchange Ato terminating exchange B are in use instead of line circuits I0 and I5,then the chain relays 50 and 52 in line equipments 22 and 24 at tandemexchange A are operated in a well-known manner to complete an obviouscircuit to relay 41, causing relay 41 to operate. At armatures 48 and49, relay 41 extends the alternating current supply from generator 5 tofilters 5| and 65 in multiple. Filter 6| is tuned to pass alternatingcurrent of 10,000 cycle frequency but not alternating current of 12,000cycle frequency. Filter 55 is tuned to pass alternating current of12,000 cycle frequency but not alternating current of 10,000 cyclefrequency. Filter 6|, therefore, causes 10,000 cycle alternating currentto be superimposed on line circuit I5 outgoing from tandem exchange A toterminating exchange B, and lter 65 causes 12,000 cycle alternatingcurrent to be superimposed on line circuit outgoing from tandem exchangeA to terminating exchange D. Filter 10 in bridge of line circuit I5 atexchange B is tuned to pass alternating current of 10,000 cyclefrequency and, therefore, causes the 10,000 cycle alternating currentlsuperimposed on line circuit I5 by means of filter 8| to be extended tobusy signal equipment 1I, which functions (in the manner similar to thatpreviously described for busy signal equipment 8|) to cause the glowingof busy signal 12. The operators at exchange B are thuswise informedthat all of the line circuits (20 and 25) outgoing from tandem exchangeA to terminating exchange C are in use. Filter 95 in bridge of linecircuit 30 at exchange D is tuned to pass alternating current o1 12,000cycle frequency and, therefore, causes the 12,000 cycle alternatingcurrent superimposed on line circuit 30 by means of lter to be extendedto busy signal equipment $5 which functions (in the manner previouslydescribed for busy signal equipment 8|) to cause the glowing of busysignal 91. The operators at exchange D are thuswise informed that all ofthe line circuits (20 and 25) outgoing from tandem exchange A toterminating exchange C are in use.

It will also be apparent that when line circuits 30 and 35 outgoing fromtandem exchange A to terminating exchange D are in use, filter 15 inexchange B will pass 12,000 cycle alternating current to busy signalequipment 16 thereby to cause the glowing of busy signal 11, and lter 85in exchange C will pass 12,000 cycle alternating current to busy signalequipment 86 thereby to cause the glowing of busy signal 81.

It will be further apparent that the line circuits outgoing from tandemexchange A to any two of the terminating exchanges B, C and D may be inuse at the same time and, therefore, there will be both 10,000 cycle and12,000 cycle alternating current superimposed on one of the linecircuits outgoing from tandem exchange A to the remaining thirdterminating exchange. Assuming now that the third terminating exchangeis exchange B, then lter 10 will pass 10,000 cycle alternating currentto busy signal equipment 1| but not 12,000 cycle alternating current,and iilter 15 will pass 12,000 cycle alternating current to busy signalequipment 16 but not 10,000 cycle alternating current. As a consequenceof the functioning of busy signal equipments 1I and 15, busy signals 12and 11 glow to respectively indicate that all of the line circuitsoutgoing from tandem exchange A to terminating exchanges C and D are inuse.

The frequencies of alternating current indicated in Fig. 2 are wellabove the upper cut-01T point of ordinary voice currents and, therefore,are superimposed on a line circuit outgoing from tandem exchange A toany one of the terminating exchanges regardlessly of whether theparticular line circuit is already in use on a telephone conversation.

It should be understood that while one embodiment of the presentinvention is disclosed and described in the preceding specification, theinvention is not limited to the particular form or application shown,but is entitled to the equivalents thereof within the scope of theappended claims.

I claim:

1. In a telephone system, first and second terminating exchanges, atandem exchange, lines from said tandem exchange to both saidterminating exchanges, said lines to said rst exchange accessible tocalls initiated in said tandem exchange or said second exchange, saidlines to said second exchange accessible to calls initiated in saidtandem exchange or said first exchange, a source of alternating current,a supervisory signal in each said terminating exchange, means responsiveto a simultaneous occupancy of all said lines to oneV of saidterminating exchanges for causing the superimposition of saidalternating current on one ofsaidlines to said other terminatingexchange, and means responsive to said superiinposition of saidalternating current for causing the supervisory signalin said otherterminating exchange to function, thereby to indicate in said otherterminating exchange that all said lines to said one terminatingexchange are occupied. i

2. InA a telephone system as claimed in claim l wherein said source ofalternating current is of a non-voice current frequency.

3. In a telephone system, rst and second terminating exchanges, a tandemexchange, lines from said tandem-exchange'to each said first and secondexchanges, means for connecting calls initiated in said tandem exchangeto idle ones or" said lines to either said first or said secondexchange, means ior connecting calls initiated in said iirst exchange toidie ones of said lines to said second exchange, means for connectingcalls initiated in said second exchange to` idle ones of said lines tosaid iirst exchange, a source of non-voice frequency alternatingcurrent, a chain circuit common to said lines to one of the terminatingexchanges operative when all said lines to said one terminating exchangeare inruse, a j

supervisory signal in the other terminating exchange, means responsiveto an operation of said chain circuit forV superimposng said alternatingcurrent on one o the lines to said other terminating exchange, and meansresponsive to said superimposing of said alternating current for causingsaid supervisory signal to operate and thereby indicate that all saidlines to said one terminating exchange are in use.. l

4. In a telephone system as claimed in claims wherein said meansresponsive to an` operation oi said chain circuit comprises a ltertunedA to pass said alternating current. Y Y

in a telephone system as claimed in claim 3 wherein said meansresponsive to anY operation of said chain `Circuit comprising a filtertuned toY pass said aiternating current,y and wherein said meansresponsive to said superimposing of said alternating current includes afilter tuned to pass said superimposed current.

caracas d. In a telephone system, a plurality of termihating oifices, atandem office, trunlrsfrom said tandeinof'ce to each of said terminatingoces; means ior completing calls between saidterminating offices oversaid trunks from said tandem oflice to said terminating offices, asource of nonvoice frequency alternating current, achain circuit cominonto the trunks from said tandem oce to one of said terminating oiiicesoperative when said trunks to said one terminating oiice becomes busy, aVlter associated with one of said trunks from said tandem office to eachoiy said other terminatingoices, said filters tuned to pass saidalternating current, a signal in each of said Yother terminating oiices,means responsive to an operation of said chain circuit for connectingsaid alternating current to. each ofl said filters thereby to cause eachsaidV filterv to extendy said alternating current toits associatedtrunk,

and means in each said associatedtrunk` responsive tcsaid extension ofsaid alternating current for causing. saidisig-nal in eachv of saidother` terminating oces to operate, therebytoindicate in all said otherofiices` that allv ci said trunks from said tandem office: to said oneterminating olce are busy. 7. In a telephone systemsfirsasecondand thirdterminating oices, a tandem oice, lines from saidy Vtandem oce to eachofsaid termina.tingY oices. means. for completing-calls from saidY tandemoiic'e tof said;v terminating offices over saidVY lines, means for.completing;I callsY between` said terminating. oices Vover said lines,alternating currents of two dierent frequencies, means rei sponsiveto asimultaneous occupancy of. all the lines to said rst terminating. cnicefor. superimposing saidv alternating. current of. one ofsaidlirequencies ion one of the lines to saidsecond terminating..offlce'and for superimposing said alternating current ofsaidotherfrequency on'one of theiines to said third'. terminating oflice,afsigmtl'V in each o said second and third terminating f oiiices, meansresponsive' to saidl super-im'posingv of. said one frequency forYope'ratingsaidsignalin saidsecond.` terminating o'ice, means responsiveg to.v saidv superrnposing. of said other frequency for operating saidsignal; in said third terminating office, saidvoperations. of saidtWosignals indicat-ing in said second and third terminating. olcesrespectively that'V all thel lines from; said'tandem office t0 said.nrst terminating oflice. arev inthe .occupied position.

8. The telephone systemv asclaimed in claim 7 wherein theV two differentfrequenciesof saidY alternating currents `are. above the: rangefoffvoicelines from said Aoice tofsaidB; C and Domces,

means for completing, calls from said A oice to. said B, C and Dofficesover said lines, means' for completingv callsbetween said. B, Cand D oflces over saidy lines, alternating currents. of twodifferentfrequencies, means. for superimposing said alternating current ofl oneof'said frequencies on one ofY said lines. to said yJD office when allsaid linesto said `IB oiIicebecome busy, means for superimposing saidalternatingcurrent ofi-said other frequency on. said one-line tol said Dollice when all saidlines to said C oiice become busy,v two busy signalsinsaid D office,A means responsive to a superimposingfof said onefrequency onsaid one line to said D office for-causing. one: of

said` busy signals tofunction, andy means responsiveto a superimposingof. said other frequency oni said one linel tosaidD` office for causingsaidy other. busy signal to function.r f'

l0. The telephone system asclaimedin claim 9. wherein said means. forsupe-rimposingk said alterhating.v current of said oneV frequencyincludes a frequency includes a lter. tuned. to pass saidv Y otherfrequency but. notsaid one frequency..

GEORGE W'. MITCHELL.

N o referencescite'd.v

